As for a network that is used, for example, as a mobile communication system, there exists the minimum device configuration required for handling traffic that flows in the network. The device configuration for the network includes, for example, a signal transfer point that is an apparatus for handling a signal transmission.
In general, there may be a trade-off relationship between a cost needed for such a signal-transmitting device allocated to the network and the transmission quality for signals that are transmitted via the signal-transmitting device. Here, for example, the cost indicates the amount of compensation that is made, by a signal-transmitting device, for degradation of transmission signals, and, hereinafter, a cost will be also expressed as “a device-cost.” In other words, the transmission quality for signals are improved when signal-transmitting devices of high costs are allocated to the network, thereby decreasing the number of signal-transmitting devices to be allocated to a communication route through which signals are transmitted. On the other hand, the total number of signal-transmitting devices to be allocated to the network increases with increasing the number of signal-transmitting devices of low costs.
Further, in the light of assuring reliability required for a network, a network configuration in which the total cost is greatly lower than the above mentioned cost required for handling traffic on the network may not be accepted.
In consideration of the above mentioned aspect required for a network configuration, when designing a network, it is preferable to approximate the total sum of device-costs for signal-transmitting devices, in other words, a cost required for constructing the network, to an objective value that is determined based on traffic that flows through each of traffic-routes on the network. In order to design a network in the above mentioned manner, a method that designs a network using an integer/linear programming method has been proposed.
Japanese Laid-open Patent Publication No. 2009-38087 discloses a method in which a method for allocating components to a board is modeled as an integer/linear programming problem, and the allocation of components is determined by solving the integer/linear programming problem.
In the case of designing a network, by solving a mathematical programming problem, such as an integer/linear programming problem, device-allocation to the network may be determined so as to minimize a cost-difference between an objective cost for a traffic-route and the total sum of device-costs of devices allocated to the traffic-route becomes minimum. Further, the mathematical programming problem allows device-allocation to be determined so that the difference between the total sum of cost-differences for a plurality of traffic-routes and an objective value (also called an objective function value) set for the network becomes minimum, thereby enabling a preferred network design.
However, there is a technical problem, in determining device-allocation to the network by solving a mathematical programming problem, that processing load needed for solving the mathematical programming problem increases with increasing the number of devices to be allocated to the network.
For example, in the case of changing the current allocation of single device among a large number of devices, an objective function value needs to be re-calculated to obtain the objective function value after changing the current allocation of the single device. Further, in order to determine whether changing the allocation of the single device is suitable for the network design, the objective function value needs to be re-calculated for all the changes of devices. This requires a large amount of processing load.